Store Game Pre-requisites Alongside Maps

[patrickmoc]

Closely related to (#682)

The website should have flags to store which game each map requires to have mounted in order for the map to function properly. This can be used by the client to detect whether or not a user has the required games installed and ready for use when loading a map.

This should be added into the Info section of the map uploader as checkboxes to mark which games are required.

[Gocnak]

This would ideally be a "required AppID mount" table that ties in with a given map info, and a map info can have 0 to many required AppID mounts.

That way when the server requests info it shows up as map.info.requiredApps

[tsa96]

Not sure exactly when we'll do this ingame, but this should be included in the 0.10.0 map submission form, it's an important thing to track from the get-go post 0.10.